"Minnesotans are accustomed to a variety of road conditions," Chief Schnell told KARE. "But the last thing we'd expect would be a thick layer of insects on the roadway."

One driver spun out on the bridge, due to the slick coating of dead mayflies, and careened across the centerline of the two-lane, undivided roadway into an oncoming car.

Fortunately the injuries were minor, and state and local authorities could focus on the huge clean-up job at hand. MnDOT sent out a plow to scrape all the mayflies off the roadway, and laid down some sand to give motorists better traction.

"The City shut off all the lights downtown," Hastings insurance agent Steve Johnson told KARE. "But I had a snow drift of mayflies in front of my office this morning. I used a shop vac to clear them all off."

When KARE encountered Johnson he was taking his mother's car to a service station automatic car wash, in hopes he could remove scores of mayflies that had been sun-baked onto the hood and roof.

"It was parked under a light last night, and was covered in mayflies," he explained. "These are just the ones that were blown off by driving the car around town."

Across the street high school student Matt Boogren was sweeping up dead mayflies in the parking lot of the Holiday convenience store where he works.

"I've been out here at least four hours," Boogren told KARE. "The sidewalk was covered with bodies of flies. We'll have to clean the windows too, because they were coated this morning."

The good news is that the siege won't last long.

The insects, which spend most of their one-year life span in the water, live only one to two days after sprouting their wings and taking flight. And they have one thing on their minds during that short burst of adulthood.

"They really have one task, and that is to find a date and mate," Jeff Hahn, a long-time University of Minnesota entomologist, told KARE.

"Both the male and females die shortly after that. It's like speed dating. They don't have any time to lose."

The adult females lay eggs before they die, which begins the mayfly life cycle all over again.

Hahn said the "mating swarm" experienced by people in the Hastings area Sunday night was more concentrated than usual. That created a virtual "insect cloud" around the bridge, where the lights were left on for traffic.

And, while the bugs be a temporary nuisance in river towns such as Hastings, huge swarms signal something positive in the environment.

"They are really good indicators for water quality," Hahn said. "That means the river is doing pretty good if we have such an abundant number of mayflies."

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